PDP-11 long ints were mixed- endian: high 16 bits, then low 16 bits. But within each half, the low 8 bits, then upper 8 bits. I was sometimes called the "NUXI" format, for how it scrambled the bytes in "UNIX".
What I was saying is that the basic PDP-11 as original designed, is a pure 16-bit machine with no 32-bit capabilities. The Unix C and other compilers used the middle-endian format for 32-bit integers largely as an artificial choice to be compatible with its FPU, as middle-endian was FPU's native long integer format. But the FPU was only a later hardware extension, and was not an inherent part of the basic system, and it's not enforced by the basic PDP-11 insturction set. It's entirely possible to modify the UNIX C compiler to store long integers in little endian.
